The present invention generally pertains to a plastic sealing element for galvanic primary cells, particularly those in the form of round cells having a metal casing and a centrally disposed carbon rod conductor, as well as a process for producing and using this plastic sealing element.
Many types of seals have been used in connection with galvanic primary cells of the Leclanche type. Most of these seals take the general form of a disk-shaped or plate-shaped plastic element, which serves as the primary component for the particular sealing arrangement which is used. Sealing elements of this general type will conventionally include a central opening for receiving the carbon rod conductor so that the zinc can is effectively sealed. An example of this basic approach may be found in DE-PS 26 19 178.
DE-AS 19 37 605 discloses a sealing element which has the conventional shape of a hollow sealing cap, but which at one (inner) side surrounds the carbon rod with a central opening (forming a sleeve), and which at the other (outer) side contacts the inner wall of the zinc can with a downwardly extending outer edge. However, above these contact zones, a peripheral space is developed which separates the sealing cap from both the carbon rod and the zinc can. As a result, before the edge of the zinc can is crimped to engage the sealing cap, this space must be filled with a sealing compound. This develops large sealing surfaces which make it more difficult for electrolyte to leak from the interior of the cell, but only at the cost of requiring additional manufacturing steps.
A cell sealing system which is considerably simpler in design is disclosed by West German Utility Model No. 19 21 573, which describes an annular rubber disk which sits on top of the plastic cover for the electrode can, and a rubber ring of the same outer diameter as the annular disk. During assembly, the lower flange-like edge of the metal positive terminal is set on the annular disk, and the rubber ring is laid on the flange-like edge. The pressure generated by crimping the metallic housing jacket leads to a slight deformation of these flexible sealing members, such that the annular disk is forced into the space between the housing jacket and the outer circumference of the flanged edge of the positive terminal. This improves electrolyte sealing with respect to the housing, but not with respect to the carbon rod, since the narrow sealing zone between the carbon rod and the annular disk represents only a limited obstacle to electrolyte leakage, particularly in view of the porous carbon material. This leaves the possibility that some electrolyte will penetrate into and be retained within the space defined between the raised center contact of the cap and the annular disk.